The objectives of the proposed research are detailed understanding of the acoustic properties of biological systems, with immediate emphasis on ultrasonic absorption and velocity dispersion in mammalian soft tissue and in solutions of important biological macromolecules. Specific objectives are: (1) measurement of the absorption and velocity of ultrasonic waves in tissues and in solutions of biopolymers, (2) identification of the physical parameters important for describing the observed behavior, (3) quantitative interpretation of the phenomena in terms of relaxation and/or other processes, and (4) continued development of appropriate instrumentation for obtaining the necessary experimental data. The attainment of these objectives would greatly increase our understanding of the physical mechanism of interaction of sound and biological systems, which must be elucidated before the full potential of the ultrasonic techniques can be realized for medical diagnostic and therapeutic applications and for biochemical and biophysical investigations of fast reactions. The results of these investigations also contribute information associated with the toxic effects and dosimetry of clinical ultrasound.